In hybrid electric vehicles (HEV), electric vehicles (EV) and the like, assembled batteries (battery systems) having a large number of battery cells of a secondary battery connected in series to each other are used in order to secure a desired high voltage. In such assembled batteries, for the purpose of the capacity calculation, or the protection and management of each battery cell, an integrated circuit that performs the measurement of a cell voltage (inter-terminal voltage of a battery cell) and the equalization (balancing) of the state, of charge, that is, remaining capacity is used in a monitoring device of the assembled battery, to thereby manage the battery cell. In such an integrated circuit, not only are cell voltage measurement and equalization performed in order to improve reliability, but also various diagnoses including the disconnection detection of cell voltage detection lines are performed to improve reliability (see, for example, PTL 1).
In recent years, assembled batteries constituted by a secondary battery such as a lithium battery have had a drastic increase in applications for electric vehicles (EV) or plug-in hybrid electric vehicles (PHV). When the secondary battery is used in the EV or PHV, since the range of use of the SOC of such a secondary battery is wider than that used in hybrid electric vehicles (REV), and a fluctuation in SOC due to a large current output is more rapid, it is required to perform the voltage monitoring and diagnoses of all the cells at high speed. In addition, for the purpose of an improvement in the accuracy of voltage monitoring and diagnoses, it is required to improve the voltage measurement accuracy of all the cells over a wide range of use of the secondary battery.
Since a circuit that measures an inter-terminal voltage of the battery cell has temperature characteristics, the temperature of the voltage measurement circuit is required to set to be in a predetermined range, in order to improve the measurement accuracy of the inter-terminal voltage.
PTL 2 discloses a capacity adjustment device of an assembled battery that changes the magnitude of a bypass current for adjusting the capacity of a large number of battery cells, on the basis of the temperature in the vicinity of a bypass resistor.
PTL 3 discloses a capacity adjustment circuit that suppresses a rise in temperature during capacity adjustment by dividing a plurality of battery cells into a plurality of groups and selecting a timing for adjusting the capacity of each battery cell for each of the groups to thereby adjust the capacity of each battery cell.